Thing is, when Jobs did it, he'd show people stuff, they'd see it, and they'd say "hey that's really cool, I could use one of those". It didn't take long at all for the iPhone to demonstrate that it had utility.
I've been buying Mac and NeXT stuff for a long time, and I have absolutely seen that work. But I've also seen cases where Apple dropped a thing I wanted, and that didn't magically change the world so I didn't want the thing.
Jobs understood that there were different users, and you had to have product differentiation and meet the needs of more than one group of users.
Also, no, the iMac G3 didn't remove even one PS/2 port, because there weren't any PS/2 ports on the Mac. It did drop other ports, and some of them were ports that were hard to replace; I had an ADB-based gizmo that needed a dongle, for instance. But for the most part, USB solved problems I cared about and made things better. It replaced a broad range of unrelated ports with a single standard port, and allowed hubs, and that was an upgrade.
USB type C doesn't do as much of that. Yeah, arguably, it is now merging power and video... But that turns out not to buy me as much. Replacing multiple kinds of serial ports, and the special ADB ports, and so on, did help some. But in that case, any given Mac might not need any serial gizmos, for instance. Losing USB type A means that basically nothing I own can be used with the new mac without specialized cables. So now I have a Type C to DisplayPort cable. DisplayPort cables worked with a bunch of different computers; the new one works only with one specific subset of Macs. The cable has no other utility. If I'm not hooking up one of the small set of USB-C macs to a displayport cable? Useless. Contrast with a USB 3 cable, which works with every computer I own *except* the USB-C Macs (that's at least a half-dozen machines including three previous macs), and works with a few dozen different devices I have. A couple of phones, at least one camera, some tablets, some external drives, you name it.
So it doesn't really feel like much of an improvement.
(That said, if it had been just the cables, I'd probably have kept the machine. But the cables, the glossy-only display option, the crappy keyboard, the loss of any kind of future-proofing upgrades down the line, losing magsafe... That was too much.)